The present invention relates to a method for connection of underwater pipelines and a tool for such connection.
Underwater conduits extending between various structures on the seabed to a floating production unit are produced in two ways. When the pipeline is a flowline for production of oil or gas, or an umbilical containing a number of conduits for checking production on the seabed, it normally extends between a manifold and the production unit. Such a pipeline may be up to several kilometres long.
Such pipelines are generally deployed on the seabed in advance independently of other equipment. When the line has to be connected to the bottom structure, its end point has to be drawn or pulled from its deployed position over to the bottom structure and the end of the pipe with the termination head is connected to a corresponding coupling head mounted on the structure.
Another type of pipeline extends between two installations on the seabed, where the installations may be wells, a manifold, a second pipeline or a branch of such a second pipeline, a so-called tee joint. The installations are located at a relatively short distance from one another, usually 20-60 metres. This type of pipeline (which is called a spool or spool piece) is fabricated on the spot in exact lengths based on measurements of the distance between the connection points, and is lowered and connected in one operation.
A common method for this type of connection is a so-called xe2x80x9cstab and hingexe2x80x9d where the spool piece is equipped with a hinge and is lowered vertically before being rotated into a horizontal position, see, for example, NO 308381.
A tool for the first type of operation is described in NO 303914. A tool frame is attached to an underwater vehicle, a so-called ROV (Remotely Operated Vehicle). The frame comprises gripping bodies for gripping and holding a pipe, together with winches for pulling the frame with a secured pipe to a connecting point. Pulling lines from the winch are attached in suitable holders mounted on the coupling head, whereupon the ROV with the tool move to the end of the pipe which is lying on the seabed some distance from the template (while the winches pay out wire). The tool is locked to the end of the pipe, whereupon the winches are started, thereby causing the tool with the secured pipe end to be pulled in towards the coupling head.
The winches are preferably individually controllable, with the result that angular deviations in the horizontal plane are adjusted during the pull-in operation, thus enabling the end of the pipe, when it is pulled in, to be axially aligned with the coupling head. The connecting point, however, is located some distance, usually 2-3 metres, above the seabed and it is therefore difficult to adjust the angular deviations in the vertical plane which are created when the pipeline has to be raised from the seabed.
A disadvantage of this type of tool is that, in order to obtain a tie-in, only small deviations, usually less than 4xc2x0, are permitted, and this can be difficult to achieve, particularly in the vertical plane.
One way of solving this problem has been to manufacture the coupling head with a downwardly directed bend or a ramp to make it easier to overcome the difference in height. The disadvantage is that it complicates standardisation and leads to increased costs.
A need therefore exists for a pull-in tool which can permit greater angular deviation during pull-in and which is capable of compensating for these deviations and adjusting the termination head so that it is correctly aligned with the coupling head.
An object of the present invention is therefore to provide a connection tool which can cope with greater vertical angular deviations during pull-in.
A second object of the invention is to provide a connection tool which can make connections more cheaply and quickly.
The tool according to the present invention is suitable for connection of pipelines to coupling heads on bottom or seabed frames or installations or to tee joints in other pipelines, as well as for connection of umbilicals.